/* trees.c -- output deflated data using Huffman coding
* Copyright (C) 1992-1993 Jean-loup Gailly
* This is free software; you can redistribute it and/or modify it under the
* terms of the GNU General Public License, see the file COPYING.
*/

/*
* PURPOSE
*
* Encode various sets of source values using variable-length
* binary code trees.
*
* DISCUSSION 
*
* The PKZIP "deflation" process uses several Huffman trees. The more
* common source values are represented by shorter bit sequences.
*
* Each code tree is stored in the ZIP file in a compressed form
* which is itself a Huffman encoding of the lengths of
* all the code strings (in ascending order by source values).
* The actual code strings are reconstructed from the lengths in
* the UNZIP process, as described in the "application note"
* (APPNOTE.TXT) distributed as part of PKWARE's PKZIP program.
*
* REFERENCES
*
* Lynch, Thomas J.
* Data Compression: Techniques and Applications, pp. 53-55.
* Lifetime Learning Publications, 1985. ISBN 0-534-03418-7.
*
* Storer, James A.
* Data Compression: Methods and Theory, pp. 49-50.
* Computer Science Press, 1988. ISBN 0-7167-8156-5.
*
* Sedgewick, R.
* Algorithms, p290.
* Addison-Wesley, 1983. ISBN 0-201-06672-6.
*
* INTERFACE
*
* void ct_init (ush *attr, int *methodp)
* Allocate the match buffer, initialize the various tables and save
* the location of the internal file attribute (ascii/binary) and
* method (DEFLATE/STORE)
*
* void ct_tally (int dist, int lc);
* Save the match info and tally the frequency counts.
*
* long flush_block (char *buf, ulg stored_len, int eof)
* Determine the best encoding for the current block: dynamic trees,
* static trees or store, and output the encoded block to the zip
* file. Returns the total compressed length for the file so far.
*
*/

#include "gzip.h"

/* ===========================================================================
* Constants
*/
/* All codes must not exceed MAX_BITS bits */
#define MAX_BITS 15

/* Bit length codes must not exceed MAX_BL_BITS bits */
#define MAX_BL_BITS 7

/* number of length codes, not counting the special END_BLOCK code */
#define LENGTH_CODES 29

/* number of literal bytes 0..255 */
#define LITERALS 256

/* end of block literal code */
#define END_BLOCK 256

/* number of Literal or Length codes, including the END_BLOCK code */
#define L_CODES (LITERALS+1+LENGTH_CODES)

/* number of distance codes */
#define D_CODES 30

/* number of codes used to transfer the bit lengths */
#define BL_CODES 19

local int near extra_lbits[LENGTH_CODES]
/* extra bits for each length code */
= {0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0};

local int near extra_dbits[D_CODES]
/* extra bits for each distance code */
= {0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 13, 13};

local int near extra_blbits[BL_CODES]
/* extra bits for each bit length code */
= {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 3, 7};

#define STORED_BLOCK 0
/* The three kinds of block type */
#define STATIC_TREES 1
/* The three kinds of block type */
#define DYN_TREES 2

#define LIT_BUFSIZE 0x2000
#ifndef DIST_BUFSIZE
#define DIST_BUFSIZE LIT_BUFSIZE
#endif
/* Sizes of match buffers for literals/lengths and distances. There are
* 4 reasons for limiting LIT_BUFSIZE to 64K:
* - frequencies can be kept in 16 bit counters
* - if compression is not successful for the first block, all input data is
* still in the window so we can still emit a stored block even when input
* comes from standard input. (This can also be done for all blocks if
* LIT_BUFSIZE is not greater than 32K.)
* - if compression is not successful for a file smaller than 64K, we can
* even emit a stored file instead of a stored block (saving 5 bytes).
* - creating new Huffman trees less frequently may not provide fast
* adaptation to changes in the input data statistics. (Take for
* example a binary file with poorly compressible code followed by
* a highly compressible string table.) Smaller buffer sizes give
* fast adaptation but have of course the overhead of transmitting trees
* more frequently.
* - I can't count above 4
* The current code is general and allows DIST_BUFSIZE < LIT_BUFSIZE (to save
* memory at the expense of compression). Some optimizations would be possible
* if we rely on DIST_BUFSIZE == LIT_BUFSIZE.
*/
#if LIT_BUFSIZE > INBUFSIZ
error cannot overlay l_buf and inbuf
#endif
/* repeat previous bit length 3-6 times (2 bits of repeat count) */
#define REP_3_6 16

/* repeat a zero length 3-10 times (3 bits of repeat count) */
#define REPZ_3_10 17

/* repeat a zero length 11-138 times (7 bits of repeat count) */
#define REPZ_11_138 18

/* ===========================================================================
* Local data
*/

/* Data structure describing a single value and its code string. */
typedef struct ct_data {
	union {
		ush freq; /* frequency count */
		ush code; /* bit string */
	} fc;
	union {
		ush dad; /* father node in Huffman tree */
		ush len; /* length of bit string */
	} dl;
} ct_data;

#define Freq fc.freq
#define Code fc.code
#define Dad dl.dad
#define Len dl.len

/* maximum heap size */
#define HEAP_SIZE (2*L_CODES+1)

local ct_data near dyn_ltree[HEAP_SIZE]; /* literal and length tree */
local ct_data near dyn_dtree[2 * D_CODES + 1]; /* distance tree */

/* The static literal tree. Since the bit lengths are imposed, there is no
* need for the L_CODES extra codes used during heap construction. However
* The codes 286 and 287 are needed to build a canonical tree (see ct_init
* below).
*/
local ct_data near static_ltree[L_CODES + 2];

local ct_data near static_dtree[D_CODES];
/* The static distance tree. (Actually a trivial tree since all codes use
* 5 bits.)
*/

/* Huffman tree for the bit lengths */
local ct_data near bl_tree[2 * BL_CODES + 1];

typedef struct tree_desc {
	ct_data near * dyn_tree; /* the dynamic tree */
	ct_data near * static_tree; /* corresponding static tree or NULL */
	int near * extra_bits; /* extra bits for each code or NULL */
	int extra_base; /* base index for extra_bits */
	int elems; /* max number of elements in the tree */
	int max_length; /* max bit length for the codes */
	int max_code; /* largest code with non zero frequency */
} tree_desc;

local tree_desc near l_desc = {
	dyn_ltree, static_ltree, extra_lbits, LITERALS + 1, L_CODES, MAX_BITS, 0
};

local tree_desc near d_desc = {
	dyn_dtree, static_dtree, extra_dbits, 0, D_CODES, MAX_BITS, 0
};

local tree_desc near bl_desc = {
	bl_tree, ( ct_data near *)0, extra_blbits, 0, BL_CODES, MAX_BL_BITS, 0
};

/* number of codes at each bit length for an optimal tree */
local ush near bl_count[MAX_BITS + 1];

/* The lengths of the bit length codes are sent in order of decreasing
* probability, to avoid transmitting the lengths for unused bit length codes.
*/
local uch near bl_order[BL_CODES] = {16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15};

local int near heap[2 * L_CODES + 1]; /* heap used to build the Huffman trees */
local int heap_len = 0; /* number of elements in the heap */
local int heap_max = 0; /* element of largest frequency */
/* The sons of heap[n] are heap[2*n] and heap[2*n+1]. heap[0] is not used.
* The same heap array is used to build all trees.
*/

/* Depth of each subtree used as tie breaker for trees of equal frequency */
local uch near depth[2 * L_CODES + 1];

/* length code for each normalized match length (0 == MIN_MATCH) */
local uch length_code[MAX_MATCH - MIN_MATCH + 1];

/* distance codes. The first 256 values correspond to the distances
* 3 .. 258, the last 256 values correspond to the top 8 bits of
* the 15 bit distances.
*/
local uch dist_code[512];

/* First normalized length for each code (0 = MIN_MATCH) */
local int near base_length[LENGTH_CODES];

/* First normalized distance for each code (0 = distance of 1) */
local int near base_dist[D_CODES];

/* DECLARE(uch, l_buf, LIT_BUFSIZE); buffer for literals or lengths */
#define l_buf inbuf

/* flag_buf is a bit array distinguishing literals from lengths in
* l_buf, thus indicating the presence or absence of a distance.
*/
local uch near flag_buf[( LIT_BUFSIZE / 8 )];

local unsigned last_lit = 0; /* running index in l_buf */
local unsigned last_dist = 0; /* running index in d_buf */
local unsigned last_flags = 0; /* running index in flag_buf */
local uch flags = 0; /* current flags not yet saved in flag_buf */
local uch flag_bit = 0; /* current bit used in flags */
/* bits are filled in flags starting at bit 0 (least significant).
* Note: these flags are overkill in the current code since we don't
* take advantage of DIST_BUFSIZE == LIT_BUFSIZE.
*/

local ulg opt_len = 0; /* bit length of current block with optimal trees */
local ulg static_len = 0; /* bit length of current block with static trees */

local ulg compressed_len = 0; /* total bit length of compressed file */

local ulg input_len = 0; /* total byte length of input file */
/* input_len is for debugging only since we can get it by other means. */

ush * file_type; /* pointer to UNKNOWN, BINARY or ASCII */
int * file_method; /* pointer to DEFLATE or STORE */

#ifdef DEBUG
extern ulg bits_sent; /* bit length of the compressed data */
extern int isize; /* byte length of input file */
#endif

extern int block_start; /* window offset of current block */
extern unsigned near strstart; /* window offset of current string */

/* ===========================================================================
* Local (static) routines in this file.
*/

local void init_block OF(( void ));
local void pqdownheap OF(( ct_data near * tree, int k ));
local void gen_bitlen OF(( tree_desc near * desc ));
local void gen_codes OF(( ct_data near * tree, int max_code ));
local void build_tree OF(( tree_desc near * desc ));
local void scan_tree OF(( ct_data near * tree, int max_code ));
local void send_tree OF(( ct_data near * tree, int max_code ));
local int build_bl_tree OF(( void ));
local void send_all_trees OF(( int lcodes, int dcodes, int blcodes ));
local void compress_block OF(( ct_data near * ltree, ct_data near * dtree ));
local void set_file_type OF(( void ));

#ifndef DEBUG
#define send_code(c, tree) send_bits(tree[c].Code, tree[c].Len)
/* Send a code of the given tree. c and tree must not have side effects */

#else /* DEBUG */
#define send_code(c, tree) \
{ if (verbose>1) fprintf(stderr,"\ncd %3d ",(c)); \
	send_bits(tree[c].Code, tree[c].Len); }
#endif

/* Mapping from a distance to a distance code. dist is the distance - 1 and
* must not have side effects. dist_code[256] and dist_code[257] are never
* used.
*/
#define d_code(dist) ((dist) < 256 ? dist_code[dist] : dist_code[256+((dist)>>7)])

#define MAX(a,b) (a >= b ? a : b)
/* the arguments must not have side effects */

/* ===========================================================================
* Allocate the match buffer, initialize the various tables and save the
* location of the internal file attribute (ascii/binary) and method
* (DEFLATE/STORE).
*/
void ct_init( ush * attr, int * methodp )
{
	int n; /* iterates over tree elements */
	int bits; /* bit counter */
	int length; /* length value */
	int code; /* code value */
	int dist; /* distance index */

	file_type = attr;
	file_method = methodp;
	compressed_len = input_len = 0L;

	if ( static_dtree[0].Len != 0 ) return; /* ct_init already called */

	/* Initialize the mapping length (0..255) -> length code (0..28) */
	length = 0;
	for ( code = 0; code < LENGTH_CODES - 1; code ++) {
		base_length[code] = length;
		for ( n = 0; n < ( 1 << extra_lbits[code] ); n ++) {
			length_code[length ++ ] = ( uch )code;
		}
	}
	/* Note that the length 255 (match length 258) can be represented
	* in two different ways: code 284 + 5 bits or code 285, so we
	* overwrite length_code[255] to use the best encoding:
	*/
	length_code[length - 1] = ( uch )code;

	/* Initialize the mapping dist (0..32K) -> dist code (0..29) */
	dist = 0;
	for ( code = 0 ; code < 16; code ++) {
		base_dist[code] = dist;
		for ( n = 0; n < ( 1 << extra_dbits[code] ); n ++) {
			dist_code[dist ++ ] = ( uch )code;
		}
	}
	dist >>= 7; /* from now on, all distances are divided by 128 */
	for ( ; code < D_CODES; code ++) {
		base_dist[code] = dist << 7;/* base dist */
		for ( n = 0; n < ( 1 <<( extra_dbits[code] - 7 )); n ++) {
			dist_code[256 + dist ++ ] = ( uch )code; /* dist code */
		}
	}

	/* Construct the codes of the static literal tree */
	for ( bits = 0; bits <= MAX_BITS; bits ++) bl_count[bits] = 0;
	n = 0;
	while ( n <= 143 ) static_ltree[n ++ ].Len = 8, bl_count[8] ++; /* 初始化 */
	while ( n <= 255 ) static_ltree[n ++ ].Len = 9, bl_count[9] ++; /* 初始化 */
	while ( n <= 279 ) static_ltree[n ++ ].Len = 7, bl_count[7] ++; /* 初始化 */
	while ( n <= 287 ) static_ltree[n ++ ].Len = 8, bl_count[8] ++; /* 初始化 */
	/* Codes 286 and 287 do not exist, but we must include them in the
	* tree construction to get a canonical Huffman tree (longest code
	* all ones)
	*/
	gen_codes(( ct_data near *)static_ltree, L_CODES + 1 );

	/* The static distance tree is trivial: */
	for ( n = 0; n < D_CODES; n ++) {
		static_dtree[n].Len = 5; /* 初始化 */
		static_dtree[n].Code = bi_reverse( n, 5 ); /* 初始化 */
	}

	/* Initialize the first block of the first file: */
	init_block();
}

/* ===========================================================================
* Initialize a new block.
*/
local void init_block()
{
	int n; /* iterates over tree elements */

	/* Initialize the trees. */
	for ( n = 0; n < L_CODES; n ++) dyn_ltree[n].Freq = 0;
	for ( n = 0; n < D_CODES; n ++) dyn_dtree[n].Freq = 0;
	for ( n = 0; n < BL_CODES; n ++) bl_tree[n].Freq = 0;

	dyn_ltree[END_BLOCK].Freq = 1;
	opt_len = static_len = 0L;
	last_lit = last_dist = last_flags = 0;
	flags = 0; flag_bit = 1;
}

#define SMALLEST 1
/* Index within the heap array of least frequent node in the Huffman tree */

/* ===========================================================================
* Remove the smallest element from the heap and recreate the heap with
* one less element. Updates heap and heap_len.
*/
#define pqremove(tree, top) \
{\
	top = heap[SMALLEST]; \
	heap[SMALLEST] = heap[heap_len--]; \
	pqdownheap(tree, SMALLEST); \
}

/* ===========================================================================
* Compares to subtrees, using the tree depth as tie breaker when
* the subtrees have equal frequency. This minimizes the worst case length.
*/
#define smaller(tree, n, m) \
	(tree[n].Freq < tree[m].Freq || \
	(tree[n].Freq == tree[m].Freq && depth[n] <= depth[m]))

/* ===========================================================================
* Restore the heap property by moving down the tree starting at node k,
* exchanging a node with the smallest of its two sons if necessary, stopping
* when the heap property is re-established (each father smaller than its
* two sons).
*/
local void pqdownheap( ct_data near * tree, int k )
{
	int v = heap[k];
	int j = k << 1; /* left son of k */
	while ( j <= heap_len ) {
		/* Set j to the smallest of the two sons: */
		if ( j < heap_len && smaller( tree, heap[j + 1], heap[j] )) j ++;

		/* Exit if v is smaller than both sons */
		if ( smaller( tree, v, heap[j] )) break;

		/* Exchange v with the smallest son */
		heap[k] = heap[j]; k = j;

		/* And continue down the tree, setting j to the left son of k */
		j <<= 1;
	}
	heap[k] = v;
}

/* ===========================================================================
* Compute the optimal bit lengths for a tree and update the total bit length
* for the current block.
* IN assertion: the fields freq and dad are set, heap[heap_max] and
* above are the tree nodes sorted by increasing frequency.
* OUT assertions: the field len is set to the optimal bit length, the
* array bl_count contains the frequencies for each bit length.
* The length opt_len is updated; static_len is also updated if stree is
* not null.
*/
local void gen_bitlen( tree_desc near * desc )
{
	ct_data near * tree = desc->dyn_tree;
	int near * extra = desc->extra_bits;
	int base = desc->extra_base;
	int max_code = desc->max_code;
	int max_length = desc->max_length;
	ct_data near * stree = desc->static_tree;
	int h; /* heap index */
	int n, m; /* iterate over the tree elements */
	int bits; /* bit length */
	int xbits; /* extra bits */
	ush f; /* frequency */
	int overflow = 0; /* number of elements with bit length too large */

	for ( bits = 0; bits <= MAX_BITS; bits ++) bl_count[bits] = 0;

	/* In a first pass, compute the optimal bit lengths (which may
	* overflow in the case of the bit length tree).
	*/
	tree[heap[heap_max]].Len = 0; /* root of the heap */

	for ( h = heap_max + 1; h < HEAP_SIZE; h ++) {
		n = heap[h];
		bits = tree[tree[n].Dad].Len + 1;
		if ( bits > max_length ) bits = max_length, overflow ++;
		tree[n].Len = ( ush )bits;
		/* We overwrite tree[n].Dad which is no longer needed */

		if ( n > max_code ) continue; /* not a leaf node */

		bl_count[bits] ++;
		xbits = 0;
		if ( n >= base ) xbits = extra[n - base];
		f = tree[n].Freq;
		opt_len += ( ulg )f * ( bits + xbits );
		if ( stree ) static_len += ( ulg )f * ( stree[n].Len + xbits );
	}
	if ( overflow == 0 ) return;

	Trace(( stderr, "\nbit length overflow\n" ));
	/* This happens for example on obj2 and pic of the Calgary corpus */

	/* Find the first bit length which could increase: */
	do {
		bits = max_length - 1;
		while ( bl_count[bits] == 0 ) bits --;
		bl_count[bits] --; /* move one leaf down the tree */
		bl_count[bits + 1] += 2; /* move one overflow item as its brother */
		bl_count[max_length] --;
		/* The brother of the overflow item also moves one step up,
		* but this does not affect bl_count[max_length]
		*/
		overflow -= 2;
	} while ( overflow > 0 );

	/* Now recompute all bit lengths, scanning in increasing frequency.
	* h is still equal to HEAP_SIZE. (It is simpler to reconstruct all
	* lengths instead of fixing only the wrong ones. This idea is taken
	* from 'ar' written by Haruhiko Okumura.)
	*/
	for ( bits = max_length; bits != 0; bits --) {
		n = bl_count[bits];
		while ( n != 0 ) {
			m = heap[ -- h];
			if ( m > max_code ) continue;
			if ( tree[m].Len != ( unsigned ) bits ) {
				Trace(( stderr, "code %d bits %d->%d\n", m, tree[m].Len, bits ));
				opt_len += (( int )bits -( int )tree[m].Len )*( int )tree[m].Freq;
				tree[m].Len = ( ush )bits;
			}
			n --;
		}
	}
}

/* ===========================================================================
* Generate the codes for a given tree and bit counts (which need not be
* optimal).
* IN assertion: the array bl_count contains the bit length statistics for
* the given tree and the field len is set for all tree elements.
* OUT assertion: the field code is set for all tree elements of non
* zero code length.
*/
local void gen_codes ( ct_data near * tree, int max_code )
{
	ush next_code[MAX_BITS + 1]; /* next code value for each bit length */
	ush code = 0; /* running code value */
	int bits; /* bit index */
	int n; /* code index */

	/* The distribution counts are first used to generate the code values
	* without bit reversal.
	*/
	for ( bits = 1; bits <= MAX_BITS; bits ++) {
		next_code[bits] = code = ( code + bl_count[bits - 1] ) << 1;
	}
	/* Check that the bit counts in bl_count are consistent. The last code
	* must be all ones.
	*/
	Assert ( code + bl_count[MAX_BITS] - 1 == ( 1 << MAX_BITS )- 1,
		"inconsistent bit counts" );
	Tracev(( stderr, "\ngen_codes: max_code %d ", max_code ));

	for ( n = 0; n <= max_code; n ++) {
		int len = tree[n].Len;
		if ( len == 0 ) continue;
		/* Now reverse the bits */
		tree[n].Code = bi_reverse( next_code[len] ++, len );

		Tracec( tree != static_ltree, ( stderr, "\nn %3d %c l %2d c %4x (%x) ",
			n, ( isgraph( n ) ? n : ' ' ), len, tree[n].Code, next_code[len] - 1 ));
	}
}

/* ===========================================================================
* Construct one Huffman tree and assigns the code bit strings and lengths.
* Update the total bit length for the current block.
* IN assertion: the field freq is set for all tree elements.
* OUT assertions: the fields len and code are set to the optimal bit length
* and corresponding code. The length opt_len is updated; static_len is
* also updated if stree is not null. The field max_code is set.
*/
local void build_tree( tree_desc near * desc )
{
	ct_data near * tree = desc->dyn_tree;
	ct_data near * stree = desc->static_tree;
	int elems = desc->elems;
	int n, m; /* iterate over heap elements */
	int max_code = - 1; /* largest code with non zero frequency */
	int node = elems; /* next internal node of the tree */

	/* Construct the initial heap, with least frequent element in
	* heap[SMALLEST]. The sons of heap[n] are heap[2*n] and heap[2*n+1].
	* heap[0] is not used.
	*/
	heap_len = 0, heap_max = HEAP_SIZE;

	for ( n = 0; n < elems; n ++) {
		if ( tree[n].Freq != 0 ) {
			heap[ ++ heap_len] = max_code = n;
			depth[n] = 0;
		} else {
			tree[n].Len = 0;
		}
	}

	/* The pkzip format requires that at least one distance code exists,
	* and that at least one bit should be sent even if there is only one
	* possible code. So to avoid special checks later on we force at least
	* two codes of non zero frequency.
	*/
	while ( heap_len < 2 ) {
		int new = heap[ ++ heap_len] = ( max_code < 2 ? ++ max_code : 0 ); /* 初始化 */
		tree[new].Freq = 1;
		depth[new] = 0;
		opt_len --; if ( stree ) static_len -= stree[new].Len;
		/* new is 0 or 1 so it does not have extra bits */
	}
	desc->max_code = max_code;

	/* The elements heap[heap_len/2+1 .. heap_len] are leaves of the tree,
	* establish sub-heaps of increasing lengths:
	*/
	for ( n = heap_len / 2; n >= 1; n --) pqdownheap( tree, n );

	/* Construct the Huffman tree by repeatedly combining the least two
	* frequent nodes.
	*/
	do {
		pqremove( tree, n ); /* n = node of least frequency */
		m = heap[SMALLEST]; /* m = node of next least frequency */

		heap[ -- heap_max] = n; /* keep the nodes sorted by frequency */
		heap[ -- heap_max] = m;

		/* Create a new node father of n and m */
		tree[node].Freq = tree[n].Freq + tree[m].Freq;
		depth[node] = ( uch ) ( MAX( depth[n], depth[m] ) + 1 );
		tree[n].Dad = tree[m].Dad = ( ush )node;
#ifdef DUMP_BL_TREE
		if ( tree == bl_tree ) {
			1 fprintf( stderr, "\nnode %d(%d), sons %d(%d) %d(%d)",
				node, tree[node].Freq, n, tree[n].Freq, m, tree[m].Freq );
		}
#endif
		/* and insert the new node in the heap */
		heap[SMALLEST] = node ++;
		pqdownheap( tree, SMALLEST );
	} while ( heap_len >= 2 );/* 堆深度判断 */

	heap[ -- heap_max] = heap[SMALLEST];

	/* At this point, the fields freq and dad are set. We can now
	* generate the bit lengths.
	*/
	gen_bitlen(( tree_desc near *)desc );

	/* The field len is now set, we can generate the bit codes */
	gen_codes (( ct_data near *)tree, max_code );
}

/* ===========================================================================
* Scan a literal or distance tree to determine the frequencies of the codes
* in the bit length tree. Updates opt_len to take into account the repeat
* counts. (The contribution of the bit length codes will be added later
* during the construction of bl_tree.)
*/
local void scan_tree ( ct_data near * tree, int max_code )
{
	int n; /* iterates over all tree elements */
	int prevlen = - 1; /* last emitted length */
	int curlen; /* length of current code */
	int nextlen = tree[0].Len; /* length of next code */
	int count = 0; /* repeat count of the current code */
	int max_count = 7; /* max repeat count */
	int min_count = 4; /* min repeat count */

	if ( nextlen == 0 ) max_count = 138, min_count = 3; /* 初始化 */
	tree[max_code + 1].Len = ( ush )0xffff; /* guard */

	for ( n = 0; n <= max_code; n ++) {
		curlen = nextlen; nextlen = tree[n + 1].Len;
		if (++ count < max_count && curlen == nextlen ) {
			continue;
		} else if ( count < min_count ) {
			bl_tree[curlen].Freq += count;
		} else if ( curlen != 0 ) {
			if ( curlen != prevlen ) bl_tree[curlen].Freq ++;
			bl_tree[REP_3_6].Freq ++;
		} else if ( count <= 10 ) { /* 长度比较 */
			bl_tree[REPZ_3_10].Freq ++;
		} else {
			bl_tree[REPZ_11_138].Freq ++;
		}
		count = 0; prevlen = curlen;
		if ( nextlen == 0 ) {
			max_count = 138, min_count = 3; /* 初始化 */
		} else if ( curlen == nextlen ) {
			max_count = 6, min_count = 3; /* 初始化 */
		} else {
			max_count = 7, min_count = 4; /* 初始化 */
		}
	}
}

/* ===========================================================================
* Send a literal or distance tree in compressed form, using the codes in
* bl_tree.
*/
local void send_tree ( ct_data near * tree, int max_code )
{
	int n; /* iterates over all tree elements */
	int prevlen = - 1; /* last emitted length */
	int curlen; /* length of current code */
	int nextlen = tree[0].Len; /* length of next code */
	int count = 0; /* repeat count of the current code */
	int max_count = 7; /* max repeat count */
	int min_count = 4; /* min repeat count */

	/* tree[max_code+1].Len = -1; */ /* guard already set */
	if ( nextlen == 0 ) max_count = 138, min_count = 3;

	for ( n = 0; n <= max_code; n ++) {
		curlen = nextlen; nextlen = tree[n + 1].Len;
		if (++ count < max_count && curlen == nextlen ) {
			continue;
		} else if ( count < min_count ) {
			do { send_code( curlen, bl_tree ); } while (-- count != 0 );
		} else if ( curlen != 0 ) {
			if ( curlen != prevlen ) {
				send_code( curlen, bl_tree ); count --;
			}
			send_code( REP_3_6, bl_tree ); send_bits( count - 3, 2 ); /* 发送到缓存 */
		} else if ( count <= 10 ) { /* 数据长度 */
			send_code( REPZ_3_10, bl_tree ); send_bits( count - 3, 3 ); /* 发送到缓存 */
		} else {
			send_code( REPZ_11_138, bl_tree ); send_bits( count - 11, 7 ); /* 发送到缓存 */
		}
		count = 0; prevlen = curlen;
		if ( nextlen == 0 ) {
			max_count = 138, min_count = 3; /* 初始化 */
		} else if ( curlen == nextlen ) {
			max_count = 6, min_count = 3; /* 初始化 */
		} else {
			max_count = 7, min_count = 4; /* 初始化 */
		}
	}
}

/* ===========================================================================
* Construct the Huffman tree for the bit lengths and return the index in
* bl_order of the last bit length code to send.
*/
local int build_bl_tree()
{
	int max_blindex; /* index of last bit length code of non zero freq */

	/* Determine the bit length frequencies for literal and distance trees */
	scan_tree(( ct_data near *)dyn_ltree, l_desc.max_code );
	scan_tree(( ct_data near *)dyn_dtree, d_desc.max_code );

	/* Build the bit length tree: */
	build_tree(( tree_desc near *)(& bl_desc ));
	/* opt_len now includes the length of the tree representations, except
	* the lengths of the bit lengths codes and the 5+5+4 bits for the counts.
	*/

	/* Determine the number of bit length codes to send. The pkzip format
	* requires that at least 4 bit length codes be sent. (appnote.txt says
	* 3 but the actual value used is 4.)
	*/
	for ( max_blindex = BL_CODES - 1; max_blindex >= 3; max_blindex --) {
		if ( bl_tree[bl_order[max_blindex]].Len != 0 ) break;
	}
	/* Update opt_len to include the bit length tree and counts */
	opt_len += 3 *( max_blindex + 1 ) + 5 + 5 + 4; /* 初始化 */
	Tracev(( stderr, "\ndyn trees: dyn %ld, stat %ld", opt_len, static_len ));

	return max_blindex;
}

/* ===========================================================================
* Send the header for a block using dynamic Huffman trees: the counts, the
* lengths of the bit length codes, the literal tree and the distance tree.
* IN assertion: lcodes >= 257, dcodes >= 1, blcodes >= 4.
*/
local void send_all_trees( int lcodes, int dcodes, int blcodes )
{
	int rank; /* index in bl_order */

	Assert ( lcodes <= L_CODES && dcodes <= D_CODES && blcodes <= BL_CODES,
		"too many codes" );
	Tracev(( stderr, "\nbl counts: " ));
	send_bits( lcodes - 257, 5 ); /* not +255 as stated in appnote.txt */
	send_bits( dcodes - 1, 5 ); /* 写入缓存 */
	send_bits( blcodes - 4, 4 ); /* not -3 as stated in appnote.txt */
	for ( rank = 0; rank < blcodes; rank ++) {
		Tracev(( stderr, "\nbl code %2d ", bl_order[rank] ));
		send_bits( bl_tree[bl_order[rank]].Len, 3 ); /* 写入缓存 */
	}
	Tracev(( stderr, "\nbl tree: sent %ld", bits_sent ));

	send_tree(( ct_data near *)dyn_ltree, lcodes - 1 ); /* send the literal tree */
	Tracev(( stderr, "\nlit tree: sent %ld", bits_sent ));

	send_tree(( ct_data near *)dyn_dtree, dcodes - 1 ); /* send the distance tree */
	Tracev(( stderr, "\ndist tree: sent %ld", bits_sent ));
}

/* ===========================================================================
* Determine the best encoding for the current block: dynamic trees, static
* trees or store, and output the encoded block to the zip file. This function
* returns the total compressed length for the file so far.
*/
ulg flush_block( char * buf, ulg stored_len, int eof )
{
	ulg opt_lenb, static_lenb; /* opt_len and static_len in bytes */
	int max_blindex; /* index of last bit length code of non zero freq */

	flag_buf[last_flags] = flags; /* Save the flags for the last 8 items */

	/* Check if the file is ascii or binary */
	if (* file_type == ( ush )UNKNOWN ) set_file_type();

	/* Construct the literal and distance trees */
	build_tree(( tree_desc near *)(& l_desc ));
	Tracev(( stderr, "\nlit data: dyn %ld, stat %ld", opt_len, static_len ));

	build_tree(( tree_desc near *)(& d_desc ));
	Tracev(( stderr, "\ndist data: dyn %ld, stat %ld", opt_len, static_len ));
	/* At this point, opt_len and static_len are the total bit lengths of
	* the compressed block data, excluding the tree representations.
	*/

	/* Build the bit length tree for the above two trees, and get the index
	* in bl_order of the last bit length code to send.
	*/
	max_blindex = build_bl_tree();

	/* Determine the best encoding. Compute first the block length in bytes */
	opt_lenb = ( opt_len + 3 + 7 )>> 3; /* 初始化 */
	static_lenb = ( static_len + 3 + 7 )>> 3; /* 初始化 */
	input_len += stored_len; /* for debugging only */

	Trace(( stderr, "\nopt %lu(%lu) stat %lu(%lu) stored %lu lit %u dist %u ",
		opt_lenb, opt_len, static_lenb, static_len, stored_len,
		last_lit, last_dist ));

	if ( static_lenb <= opt_lenb ) opt_lenb = static_lenb;

	/* If compression failed and this is the first and last block,
	* and if the zip file can be seeked (to rewrite the local header),
	* the whole file is transformed into a stored file:
	*/
	if ( stored_len <= opt_lenb && eof && compressed_len == 0L && seekable()) {
		/* Since LIT_BUFSIZE <= 2*WSIZE, the input data must be there: */
		if ( buf == ( char *)0 ) error ( "block vanished" );

		copy_block( buf, ( unsigned )stored_len, 0 ); /* without header */
		compressed_len = stored_len << 3; /* 压缩长度 */
		* file_method = STORED;
	} else if ( stored_len + 4 <= opt_lenb && buf != ( char *)0 ) { /* 4: two words for the lengths */
		/* The test buf != NULL is only necessary if LIT_BUFSIZE > WSIZE.
		* Otherwise we can't have processed more than WSIZE input bytes since
		* the last block flush, because compression would have been
		* successful. If LIT_BUFSIZE <= WSIZE, it is never too late to
		* transform a block into a stored block.
		*/
		send_bits(( STORED_BLOCK << 1 )+ eof, 3 ); /* send block type */
		compressed_len = ( compressed_len + 3 + 7 ) & ~ 7L; /* 压缩长度 */
		compressed_len += ( stored_len + 4 ) << 3; /* 压缩长度 */

		copy_block( buf, ( unsigned )stored_len, 1 ); /* with header */
	} else if ( static_lenb == opt_lenb ) {
		send_bits(( STATIC_TREES << 1 )+ eof, 3 ); /* 发送到缓存 */
		compress_block(( ct_data near *)static_ltree, ( ct_data near *)static_dtree );
		compressed_len += 3 + static_len;/* 块压缩 */
	} else {
		send_bits(( DYN_TREES << 1 )+ eof, 3 ); /* 发送到缓存 */
		send_all_trees( l_desc.max_code + 1, d_desc.max_code + 1, max_blindex + 1 );
		compress_block(( ct_data near *)dyn_ltree, ( ct_data near *)dyn_dtree );
		compressed_len += 3 + opt_len; /* 压缩长度 */
	}
	Assert ( compressed_len == bits_sent, "bad compressed size" );
	init_block();

	if ( eof ) {
		Assert ( input_len == isize, "bad input size" );
		bi_windup();
		compressed_len += 7; /* align on byte boundary */
	}

	return compressed_len >> 3; /* 压缩长度 */
}

/* ===========================================================================
* Save the match info and tally the frequency counts. Return true if
* the current block must be flushed.
*/
int ct_tally ( int dist, int lc )
{
	l_buf[last_lit ++ ] = ( uch )lc;
	if ( dist == 0 ) {
		/* lc is the unmatched char */
		dyn_ltree[lc].Freq ++;
	} else {
		/* Here, lc is the match length - MIN_MATCH */
		dist --; /* dist = match distance - 1 */
		Assert(( ush )dist < ( ush )MAX_DIST &&
			( ush )lc <= ( ush )( MAX_MATCH - MIN_MATCH ) &&
			( ush )d_code( dist ) < ( ush )D_CODES, "ct_tally: bad match" );

		dyn_ltree[length_code[lc] + LITERALS + 1].Freq ++;
		dyn_dtree[d_code( dist )].Freq ++;

		d_buf[last_dist ++ ] = ( ush )dist;
		flags |= flag_bit;
	}
	flag_bit <<= 1;

	/* Output the flags if they fill a byte: */
	if (( last_lit & 7 ) == 0 ) {
		flag_buf[last_flags ++ ] = flags;
		flags = 0, flag_bit = 1;
	}
	/* Try to guess if it is profitable to stop the current block here */
	if ( level > 2 && ( last_lit & 0xfff ) == 0 ) {
		/* Compute an upper bound for the compressed length */
		ulg out_length = ( ulg )last_lit * 8L;
		ulg in_length = ( ulg )strstart - block_start;
		int dcode;
		for ( dcode = 0; dcode < D_CODES; dcode ++) {
			out_length += ( ulg )dyn_dtree[dcode].Freq *( 5L + extra_dbits[dcode] );/* 轮询 */
		}
		out_length >>= 3; /* 输出长度 */
		if ( last_dist < last_lit / 2 && out_length < in_length / 2 ) return 1;/* 长度判断 */
	}
	return ( last_lit == LIT_BUFSIZE - 1 || last_dist == DIST_BUFSIZE );
	/* We avoid equality with LIT_BUFSIZE because of wraparound at 64K
	* on 16 bit machines and because stored blocks are restricted to
	* 64K-1 bytes.
	*/
}

/* ===========================================================================
* Send the block data compressed using the given Huffman trees
*/
local void compress_block( ct_data near * ltree, ct_data near * dtree )
{
	unsigned dist; /* distance of matched string */
	int lc; /* match length or unmatched char (if dist == 0) */
	unsigned lx = 0; /* running index in l_buf */
	unsigned dx = 0; /* running index in d_buf */
	unsigned fx = 0; /* running index in flag_buf */
	uch flag = 0; /* current flags */
	unsigned code; /* the code to send */
	int extra; /* number of extra bits to send */

	if ( last_lit != 0 ) do {
		if (( lx & 7 ) == 0 ) flag = flag_buf[fx ++ ]; /* 标志 */
		lc = l_buf[lx ++ ];
		if (( flag & 1 ) == 0 ) {
			send_code( lc, ltree ); /* send a literal byte */
			Tracecv( isgraph( lc ), ( stderr, " '%c' ", lc ));
		} else {
			/* Here, lc is the match length - MIN_MATCH */
			code = length_code[lc];
			send_code( code + LITERALS + 1, ltree ); /* send the length code */
			extra = extra_lbits[code];
			if ( extra != 0 ) {
				lc -= base_length[code];
				send_bits( lc, extra ); /* send the extra length bits */
			}
			dist = d_buf[dx ++ ];
			/* Here, dist is the match distance - 1 */
			code = d_code( dist );
			Assert ( code < D_CODES, "bad d_code" );

			send_code( code, dtree ); /* send the distance code */
			extra = extra_dbits[code];
			if ( extra != 0 ) {
				dist -= base_dist[code];
				send_bits( dist, extra ); /* send the extra distance bits */
			}
		} /* literal or match pair ? */
		flag >>= 1;
	} while ( lx < last_lit );

	send_code( END_BLOCK, ltree );
}

/* ===========================================================================
* Set the file type to ASCII or BINARY, using a crude approximation:
* binary if more than 20% of the bytes are <= 6 or >= 128, ascii otherwise.
* IN assertion: the fields freq of dyn_ltree are set and the total of all
* frequencies does not exceed 64K (to fit in an int on 16 bit machines).
*/
local void set_file_type()
{
	int n = 0;
	unsigned ascii_freq = 0;
	unsigned bin_freq = 0;
	while ( n < 7 ) bin_freq += dyn_ltree[n ++ ].Freq; /* 初始化 */
	while ( n < 128 ) ascii_freq += dyn_ltree[n ++ ].Freq; /* 初始化 */
	while ( n < LITERALS ) bin_freq += dyn_ltree[n ++ ].Freq;
	* file_type = bin_freq > ( ascii_freq >> 2 ) ? BINARY : ASCII; /* 设置文件打开方式 */
	if (* file_type == BINARY && translate_eol ) {
		warn( "-l used on binary file", "" );
	}
}
